Compositions and methods for thermally shaping hair typically result in the degradation of one or more mechanical properties of the treated hair fibers, e.g., their strength, due to the use of harsh chemicals and/or the relatively high temperatures of the shaping methods themselves. The recent introduction of high temperature flat irons (T>150° C.) has encouraged the use of increasingly higher hair shaping temperatures. For example, high temperature ironing temperatures are utilized by hair salons in the thermal hair shaping method known as “Brazilian Blowout”. This method consists of applying a hair treatment composition followed by a high temperature step employing a flat iron. When the hair treatment composition contains formaldehyde or formaldehyde precursor that releases formaldehyde at the ironing temperature, the crosslinking resulting from the reaction of the formaldehyde with hair keratin reduces or minimizes the heat-induced weakening of the treated hair fibers. The straightening quality and hair aesthetics obtained by application of the Brazilian Blowout method are clearly superior to those achieved by the use of conventional chemical hair relaxers. However, due to health concerns, the use of formaldehyde keratin crosslinkers is undergoing greater scrutiny and may become subject to regulatory restriction.
In contemplation of the reduction, if not discontinuance, of aldehydic keratin crosslinkers in hair treatment compositions and methods, whether induced voluntarily or by government regulation, there has arisen a need for a composition and method for the thermal shaping of hair that avoids or greatly limits the use of formaldehyde keratin crosslinkers but reduces or lessens the extent of damage to hair fibers, manifested as a reduction in the tensile strength of the thermally shaped hair fibers, in a manner that is at least as effective as the hair treatment compositions and thermal hair shaping methods they are intended to replace.
All thermal methods for the thermal shaping of hair result in some measurable reduction in tensile strength of the shaped hair fibers, the higher the hair shaping temperature generally accompanied by a correspondingly greater reduction in hair fiber strength.
There is thus a need for a hair fiber strengthening composition that will more effectively limit the extent of the reduction in hair fiber strength that accompanies the use of known and conventional thermal hair treatment compositions and methods such as Brazilian Blowout.